neuroimaging and cognitive tests to measure brain
changes and memory, plus a mathematical model that
incorporated two sources of environmental air-quali-
ty data.
“What we found was that women with the highest
exposure to pollutants showed an early decline in epi-
sodic memory,” he says. This type of long-term memory
involves recalling a previous experience along with the
time and place of the event and associated emotions. The
decline Chen detected in these women appeared preclin-
ically—before any actual symptoms of Alzheimer’s—and
was independent of the subjects’ cardiovascular status.
Alzheimer’s research has established that people with a
decline in episodic memory have a very high risk of devel-
oping the full-blown disease later in life.
“There are more than 10 studies that link late-life
exposure to air pollution and dementia,” Chen says. “The
evidence there is quite compelling. Whether exposure in
early life is also a factor, we don’t know. But in animal
studies, toxicologists start exposure in early life, look at
the pathological changes and see problems. It looks like
small particles can accelerate the amyloid-deposit pro-
cess, but we’re not yet sure whether this happens in
humans. And there might be a genetic component
involved—that is, some people might be more suscepti-
ble than others to the effect of pollution. There might be
a subgroup of individuals who are particularly suscepti-
ble and might be at greater risk. We don’t yet have enough
power in our studies to address this question, but I
believe we will.”
RISK REDUCTION
while the disease reMains a horror facing millions of
people around the globe, there is some encouraging
news in these discoveries about air pollution, several
scientists say: people can take action to diminish the
hazards. Most drugs so far have not helped patients,
says George Washington University epidemiologist
Melinda Power, who focuses on identifying modifiable
risk factors for cognitive decline and dementia. ”So at
the moment, prevention through the reduction of envi-
ronmental and lifestyle factors looks like our best bet,”
she says. “And air-pollution exposure is looking [like it
could be] very important.”
The evidence about brain damage is a strong argu-
ment for stricter air-quality controls, says University of
Michigan epidemiologist Kelly Bakulski. “This is a real-
ly hopeful area,” he says. “Unlike our genes, environ-
mental factors are things we can control—removing
these pollutants from our communities will have no ill
and many positive impacts.”
In addition, Gatz says that simple changes in how
we live can help. “Physical exercise is shown to reduce
risk,” she says, both because it increases blood flow to
the brain and because it increases levels of brain-
derived neurotrophic factor, a protein that promotes
the growth and maintenance of brain cells.
Knowing the havoc that the disease inflicts, it is time
to take such changes seriously. “We have the means to
do it,” Bakulski says, “and given the risk of not doing it,
we must.”“THE WAY FORWARD”
Proinflammatory Cytokines, Aging,
and Age-Related Diseases. M. Michaud
et al. in Journal of the American Medical
Directors Association, Vol. 14, No. 12,
pages 877–882; December 2013.
Cryo-EM Structures of Tau Filaments
from Alzheimer’s Disease. A .W. P.
Fitzpatrick et al. in Nature, Vol. 547,
pages 185–190; July 17, 2017.
Memory Engrams: Recalling the Past
and Imagining the Future. Sheena A.
Josselyn and Susumu Tonegawa
in Science, Vol. 367, Article No. eaaw4325;
January 3, 2020.
FROM OUR ARCHIVES
New Strategy for Alzheimer’s.
Howard M. Fillit; February 2019.“THE MENOPAUSE CONNECTION”
How Would We Combat Menopause as
an Alzheimer’s Risk Factor? Lisa Mosconi
and Roberta Diaz Brinton in Expert Review
of Neurotherapeutics, Vol. 18, No. 9,
pages 689–691; 2018.
Understanding the Impact of Sex and
Gender in Alzheimer’s Disease: A Call
to Action. Rebecca A. Nebel et al. in
Alzheimer’s & Dementia: The Journal of
the Alzheimer’s Association, Vol. 14, No. 9,
pages 1171–1183; September 2018.
Estrogens and Memory: Basic Research
and Clinical Implications. Edited by
Karyn Frick. Oxford University
Press, 2020.
The XX Brain: The Groundbreaking
Science Empowering Women to
Maximize Cognitive Health and Prevent
Alzheimer’s Disease. Lisa Mosconi.
Penguin Random House, 2020.
FROM OUR ARCHIVES
Preventing Prions. By Sonia Minikel
Vallabh and Eric Vallabh Minikel;
March 2020.“THE ROLE OF AIR POLLUTION”
Alzheimer’s Disease and Alpha-Synuclein
Pathology in the Olfactory Bulbs of
Infants, Children, Teens and Adults
≤ 40 Years in Metropolitan Mexico
City: APOE4 Carriers at Higher Risk
of Suicide Accelerate Their Olfactory
Bulb Pathology. L. Calderón-Garcidueñas
et al. in Environmental Research, Vol. 166,
pages 348–362; October 2018.
Particulate Matter Air Pollution, Physical
Activity and Systemic Inflammation
in Taiwanese Adults. Z. Zhang et al.
in International Journal of Hygiene and
Environmental Health, Vol. 221, No. 1,
pages 41–47; January 2018.
Particulate Matter and Episodic Memory
Decline Mediated by Early Neuro-
anatomic Biomarkers of Alzheimer’s
Disease. D. Younan et al. in
Brain, Vol. 143, No. 1, pages 289–302;
January 2020.
FROM OUR ARCHIVES
The Metabolism of Cities. Abel Wolman;
September 1965.More to Explore on Alzheimer’s Disease
scientificamerican.com/magazine/saMay 2020, ScientificAmerican.com 47Research papers and
archival coverage related
to the articles in this
special report.